Process for producing aldehydes by hydroformylation of olefins

ABSTRACT

A process for the preparation of aldehydes or aldehydes and alcohols by hydroformylation of olefins containing more than 3 carbon atoms comprising a hydroformylation stage, in which the olefin is hydroformylated under a pressure of from 50 to 1000 bar and at a temperature of from 50° to 180° C. using a rhodium catalyst that is dissolved in a homogeneous reaction medium and by extraction of the rhodium catalyst, in which 
     a) the hydroformylation is carried out in the presence of a rhodium complex, which exhibits, as ligand, a polydentate, organic nitrogen compound that is free from phosphorus and capable of forming complexes with Group VIII metals, which additionally contains at least one tertiary nitrogen radical that is capable of being protonized by a weak acid, 
     b) the effluent of the hydroformylation stage is subjected to extraction with an aqueous solution of a distillable acid optionally following separation or partial separation of aldehydes and alcohols, 
     (c) the aqueous acid extract is subjected to thermal treatment in the presence of an organic solvent or solvent mixture, which is inert under the hydroformylation conditions, with distillation of the aqueous acid, by means of which treatment the complex is deprotonized and transferred to the organic phase, and 
     (d) the organic phase containing the catalyst complex is recycled to the hydroformylation stage.

This is the U.S. National Stage Applications if PCT/EP97/00372 filedJan. 28, 1997.

DESCRIPTION

The invention relates to a process for the preparation of aldehydes oraldehydes and alcohols by hydroformylation of olefins containing morethan 3 carbon atoms and recovery of the catalyst by a combination of (1)recycling the distillation bottoms following the removal, bydistillation, of the hydroformylation products and (2) extracting thecatalyst complex with aqueous solutions of weak acids whose polydentatenitrogenous ligand additionally contains at least one tertiary nitrogenradical protonizable with weak acids.

The hydroformylation of olefins with carbon monoxide and hydrogen in thepresence of transition metal catalysts is well known. While α-olefinsare capable of hydroformylation to a high degree usingrhodium-containing catalysts (cf J. Falbe, Ed.: New Syntheses WithCarbon Monoxide, Springer, Berlin 1980, pp. 55 et seq), this catalystsystem is less suitable for internal and internal, branched-chainolefins and also for olefins containing more than 7 carbon atoms (cfFalbe, pp. 95 et seq). Thus internal carbon-carbon double bonds arehydroformylated in the presence of such a catalyst only very slowly.Since the separation of the hydroformylation product from thehomogeneous catalyst dissolved in the reaction system usually takesplace by distillation and the boiling point of the aldehyde formedduring hydroformylation increases with increasing carbon number andchain length to temperatures at which the rhodium-containing catalystdecomposes, this hydroformylation method is uneconomical for thehydroformylation of olefins containing more than 7 carbon atoms. In thehydroformylation of polymeric olefins such as polyisobutene, the noblemetal-containing catalyst cannot be recovered in a reusable form.

On the other hand internal and internal, branched-chain olefins can beadvantageously hydroformylated with so-called "bare" rhodium, ie withhomogeneous rhodium compounds dissolved in the hydroformylation mediumand not modified with phosphorous ligands such as phosphines orphosphites. Such rhodium catalysts not modified with phosphines orphosphites and their suitability as catalysts for the hydroformylationof the aforementioned classes of olefins are known (cf Falbe, pp. 38 etseq). The terms "bare rhodium" or "bare rhodium catalysts" are used inthis application for rhodium hydroformylation catalysts which are notmodified, under the conditions of the hydroformylation, with ligands andparticularly not with phosphorous ligands such as phosphine or phosphiteligands, unlike conventional rhodium hydroformylation catalysts.Carbonyl or hydrido ligands are not to be regarded as ligands in thiscontext. It is assumed in the technical literature (cf Falbe, pp. 38 etseq), that the rhodium compound HRh(CO)₄ is the catalytically activerhodium species in the hydroformylation using "bare rhodium catalysts",although this is not absolutely proven on account of the many chemismsconcurrently taking place in the hydroformylation reaction zone. Onlyfor the sake of simplicity do we also go by this assumption in thepresent application, without this imposing any restriction on the scopeof the invention, if at some time in the future a rhodium species otherthan that stated should turn out to be the actual catalytically activespecies. The "bare rhodium catalysts" form under the conditions of thehydroformylation reaction from rhodium compounds, eg rhodium salts, suchas rhodium(III) chloride, rhodium(III) nitrate, rhodium(III) acetate,rhodium(II) acetate, rhodium(III) sulfate, or rhodium(III) ammoniumchloride, from rhodium chalkogenides, such as rhodium(III) oxide orrhodium(III) sulfide, from salts of rhodium oxyacids, for example therhodates, from rhodium carbonyl compounds, such as Rh₄ (CO)₁₂ and Rh₆(CO)₁₆ or from organorhodium compounds, such as rhodium dicarbonylacetylacetonate, cyclooctadiene rhodium acetate or chloride in thepresence of CO/H₂ mixtures, generally designated as synthesis gas. Forinformation on the execution of hydroformylations with "bare" rhodiumreference may be made, at this juncture, to the following literature byway of example: U.S. Pat. No. 4,400,547; DE-A 3338340; DE-A 2604545; WO82/03856; Chem. Ber. 102, 2238 (1969); Tetrahedron Lett. 29, 3261(1968); Hydrocarbon Process. 85-86 (1975).

However hydroformylation using "bare" rhodium also suffers from thedrawback that the thermolabile rhodium catalyst (cf U.S. Pat. No.4,400,547) partially decomposes to metallic rhodium on account of thethermal load imposed during purification, by distillation, of thehydroformylation product, which is deposited on the walls of the reactorand pipes. The precipitated metallic rhodium cannot be recycled to thehydroformylation reaction, since it cannot be converted back to thecatalytically active rhodium compound under the hydrotormylationconditions. The rhodium losses resulting from this chemical behavior of"bare rhodium catalysts" have hitherto prevented any large-scaleoperation of this process.

DE-A 3,338,340 and U.S. Pat. No. 4,400,547 describe processes forhydroformylation using "bare rhodium catalysts", in which a phosphine orphosphite is added to the effluent of the hydroformylation for theprevention of the deposition of rhodium and to protect the rhodiumcatalyst from thermal disintegration during purification, bydistillation, of the hydroformylation product stream by the formation ofphosphine or phosphite complexes. On completion of distillation therhodium-containing distillation bottoms are treated with an oxidizingagent, in which case the rhodium is liberated in catalytically activeform from the relevant phosphine or phosphite complexes and thephosphine or phosphite ligands are oxidized to the correspondingphosphine oxides and phosphates not capable of forming rhodium complexesunder the hydroformylation conditions. The oxidized distillation bottomsare then used again as catalyst for the hydroformylation. The oxidizedphosphorus compounds formed during the oxidation are not usuallyundesirable during hydroformylation, but the peculiarities of theprocess are such that the oxidized phosphorus compounds accumulate inthis hydroformylation circuit, for which reason a partial stream of thiscatalyst solution must be constantly removed from the hydroformylationcircuit and replenished by fresh catalyst solution. The removed catalystsolution must be subjected to a separate procedure for the recovery therhodium that is present therein.

WO 82/03856 relates to a process for the thermostabilization ofunmodified, that is to say "bare rhodium catalysts", in which theeffluent of the hydroformylation reaction is treated with anoxygen-containing gas, by which means aldehydes formed are partiallyoxidized to the corresponding carboxylic acids, which form thermostablerhodium carboxylates with the rhodium catalyst during purification bydistillation, which carboxylates can be reused as catalysts for thehydroformylation. A disadvantage of this process is the reduction of theyield as a result of the partial oxidation of the desired aldehyde tocarboxylic acids. Furthermore this process is restricted to thosehydroformylatlons in which distillable products are formed. Thus, forexample, in this process, the rhodium catalyst cannot be separated fromthe hydroformylation product of polyisobutene.

Hydroformylations with inter alia cobalt and rhodium in the presence ofpolydentate, nitrogenous ligands containing at least two nitrogenradicals, such as bipyridine and N,N,N',N'-tetramethylethylenediamine,are described in U.S. Pat. No. 3,594,425. These ligands effectstabilization of the catalyst during purification by distillation withsubsequent catalyst recycling, in the so-called "residues mode". Oncompletion of the distillation the rhodium-containing distillationbottoms are used again as catalyst for the hydroformylation. Thehigh-boilers formed during the hydroformylation and by distillativepurification are not usually undesirable during hydroformylation, butthe peculiarities of the process are such that the oxidized phosphoruscompounds accumulate in this hydroformylation circuit, for which reasona partial stream of this catalyst solution must be constantly removedfrom the hydroformylation circuit and replenished by fresh catalystsolution. The removed catalyst solution must be subjected to a separateprocedure for the recovery of the rhodium present therein.

Furthermore this process is restricted to those hydroformylations inwhich distillable products are formed. Thus, for example, in thisprocess, the rhodium catalyst cannot be separated from thehydroformylation product of polyisobutene.

Rhodium complexes with polydentate, nitrogenous ligands are alsodescribed as catalysts for hydroformylations in JP-A 262,086 (1994). Ahigh selectivity toward branched-chain products is reported to be aspecial property of such systems.

U.S. Pat. No. 4,298,499 describes the introduction of nitrogenousligands such as bipyridine to an oxo-effluent, with the intention ofpreventing precipitation of rhodium during the purification bydistillation. The hydroformylation itself was carried out in thepresence of a tertiary amine for specific formation of alcohols.Following the extraction of the amine, the introduction of inter alianitrogenous ligands is intended to effect separation of rhodium withoutdeposition of rhodium. The distillation bottoms are then recycled ascatalyst to the hydroformylation zone. However, this suffers from theaforementioned drawback of the "residues mode", namely the necessity toremove a portion of the residues which has to be worked up to recoverthe rhodium.

Finally, EP 621,075 reveals a reversible extraction of tertamine-substituted triaryl phosphines. In particular, said referencedescribes an extraction using aqueous solutions containing carbonicacids. Depressurization of the solution again yielded a catalyst whichis soluble in the organic medium. This concept of the use ofamine-substituted aryl phosphines is encumbered with drawbacks, since,firstly, side reactions such as the oxidation of triaryl phosphine totriaryl phosphine oxide using rhodium catalysts in the presence of CO₂are known and, secondly, yield losses caused by double bondisomerization are to be expected. Finally, internal double bonds arehydroformylated by Rh/phosphine only very slowly. Further, the tertamine-substituted phosphines are difficult to prepare

It is thus an object of the present invention to find a process for thepreparation of aldehydes from internal and/or branched-chain olefinsusing "bare rhodium catalysts", which does not suffer from the abovedrawbacks and by means of which the said problems relating to thedeposition of metallic rhodium during purification, by distillation, ofthe hydroformylation product and the separation of rhodium catalyst fromundistillable desired aldehydes or from high-boilers peculiar to thereaction can be satisfactorily solved.

The invention solves this problem by means of a process for thepreparation of aldehydes or aldehydes and alcohols by hydroformylationof olefins containing more than 3 carbon atoms, including ahydroformylation stage, in which the olefin is hydroformylated under apressure of from 50 to 1000 bar and at a temperature of from 50° to 180°C. using a rhodium catalyst that is dissolved in a homogeneous reactionmedium, and a catalyst recovery stage involving extraction of therhodium catalyst, in which

a) the hydroformylation is carried out in the presence of a rhodiumcomplex which contains, as ligand, a polydentate, organic nitrogencompound that is free from phosphorus and capable of forming complexeswith Group VIII metals, which compound additionally contains at leastone tertiary nitrogen radical that is capable of being protonized by aweak acid,

b) the effluent of the hydroformylation stage, is subjected, optionallyfollowing separation or partial separation of aldehydes and alcohols, toextraction with an aqueous solution of a distillable acid,

(c) the aqueous acid extract is subjected to heat treatment in thepresence of an organic solvent or solvent mixture which is inert underthe hydroformylation conditions, with distillation of the aqueous acid,by means of which treatment the complex is deprotonized and transferredto the organic phase, and

(d) the organic phase containing the catalyst complex is recycled to thehydroformylation stage.

This novel process surprisingly yields excellent results not only asregards the simple method of catalyst recovery, but also on account ofthe high yields of aldehydes compared with alcohols, even at lowhydroformylation temperatures, whereas it would have been expected fromU.S. Pat. No. 4,298,499 and Chem. Ing. Techn. 44, 708, (1972) that thealdehyde yield would, in the presence of ligands containing tert-aminegroups, be relatively small and thus not sufficient for a large-scaleprocess.

According to the invention, the ligands used are primarily bifunctionalpolydentate organic nitrogen compounds containing at least two nitrogenatoms capable of forming a complex with Group VIIIB transition metalsand which additionally contain at least one tertiary amine group capableof being protonized.

Due to the action of these ligands there are formed coordinate bondswith the central rhodium atom of the rhodium catalyst--presumably viathe free electron pairs of the nitrogen atoms. Such compounds are knownas chelating agents. The presence of at least one tertiary amino groupwhich is protonizable and is not attached to the central rhodium atom ofthe rhodium catalyst, is a determining factor for the feasibility of theprocess of the invention.

In particular, use is made of the novel compounds of the formula 1:##STR1## In which X denotes a bridging member selected from the groupconsisting of a covalent bond, methylene, ethylene, oxo, thio,alkylimino, and arylimino and the radicals R independently denotehydrogen, alkyl radicals containing from 1 to 18 carbon atoms, or alkoxyradicals containing from 1 to 18 carbon atoms, where these radicals canbe part of a saturated or unsaturated ring and where at least one of theradicals R or optionally of the substituents on a ring formed by thealkyl or alkoxy radicals is a radical of the formula: ##STR2## in whichn denotes an integer from 0 to 20 and R' denotes alkyl, cycloalkyl,aralkyl, or aryl radicals containing up to 18 carbon atoms, where theradicals R' can be bridged together.

Other suitable ligands are polyamines of the formula 2: ##STR3## whereR" denotes hydrogen alkyl, cycloalkyl, aryl, or aralkyl radicals, whichcan in turn carry dialkylamino radicals and m denotes an integer from 2to 35000, provided that when R" denotes hydrogen at least some of thehydrogen atoms are substituted by alkyl carbonyl containing from 2 to 18carbon atoms or by hydroxy(alkoxy)alkyl radicals obtained by thereaction of the secondary amino group with from 1 to 10 mol of ethyleneoxide or from 1 to 10 mol of propylene oxide and further provided thatthe polyamine contains at least 3 tertiary nitrogen atoms that arecapable of being protonized.

Particularly preferred are tert-amine-substituted bipyridines of theformula 3: ##STR4## in which the radicals R have the meanings stated forformula 1 and which carry at least one radical containing a tertiaryamino group and having the formula: ##STR5## in which n and R' have theaforementioned meanings.

Representative examples are the ligands 1 and 2 and their positionalisomers 1' and 2' and also compounds substituted by further inertsubstituents. ##STR6##

To illustrate the large number of ligands to be used in the process ofthe invention a number of further nitrogenous chelating agents ismentioned below by way of example, which can be used in the process ofthe invention following the introduction of an additional tertiary aminogroup.

2,2'-Biquinolines such as ligand 3: ##STR7##5,6,5',6'-Dibenzo-2,2'-biquinolines such as ligand 4: ##STR8##1,10-Phenanthrolines, 2,9-dimethyl phenanthrolines,4,7-diphenyl-1,10-phenanthrolines, such as ligand 5("bathophenanthroline"): ##STR9##2,9-Dimethyl-4,7-diphenyl-1,10-phenanthrolines such as ligand 6("bathocuproine"): ##STR10## 4,5-Diazofluorenes such as ligand 7:##STR11## Dipyrido-(3,2-a:2',3'-c)phenazines such as ligand 9: ##STR12##(ligands 7 and 8 can be obtained as described in Aust. J. Chem., 23,1023, (1970))

2,2',6',2"-Terpyridines such as ligand 9: ##STR13##4'-Phenyl-2,2',6',2"-terpyridines such as ligand 10: ##STR14##4-Methyl-(4'-phenyl)-(4"-methyl)-2,2',6',2"-terpyridines such as ligand11: ##STR15##

Other suitable polydentate ligands containing nitrogen are bipyrroles,bipyrazoles, bisimidazoles, bitriazoles, bitetrazoles, bipyridazines,bipyrim idines, bipyrazines, bitriazines, and also the porphines. Theligands can be asymmetrical, if desired, for example produced by linkingan imidazole to a pyridine. The hydroformylation with the rhodiumcomplex with the polydentate nitrogenous ligands takes place under knownconditions. It is generally carried out at temperatures ranging from 60to 180° C., preferably from 80 to 140° C., and more preferably from 90to 130° C. and under a pressure generally of from 50 to 1000 bar,preferably from 70 to 500 bar, and more preferably from 100 to 400 bar.The hydroformylation otherwise takes place under conditions as areusually used for hydroformylations using "bare" rhodium and as aredescribed for example in the literature cited above relating tohydroformylation using "bare" rhodium.

The pressure and temperature conditions used in the hydroformylationstage and the composition of the synthesis gas can be varied toinfluence the product ratio alcohol/aldehyde in the hydroformylationproduct stream for example, for given synthesis gas compositions--molarratio of CO:H_(s) 50:50, 40:60 and 60:40 respectively--, thehydroformylation of trimerpropylene--carried out at a temperature of130° C. and under a pressure of 280 bar--there is attained a molar ratioof aldehyde to alcohol of 93:7 in each case. When the temperature isincreased from 130° C. to 150° C. the molar ratio of aldehyde to alcoholin the hydroformylation product stream changes as a function of thesynthesis gas composition--CO:H₂ molar ratio 50:50, 40:60, and 60:40--to76:24, 67:33, and 82:18 respectively.

The hydroformylation can be carried out in the presence or absence oforganic solvents. The use of organic solvent is particularlyadvantageous, especially in the hydroformylation of long-chain orpolymeric olefins. The solvents used can be those usually employed inhydroformylation processes, for example high-boiling aromatic andaliphatic hydrocarbons or high-boiling aldehyde condensation productsformed during the hydroformylation reaction as by-products resultingfrom the condensation of the aldehydes produced.

The effluent from the hydroformylation stage is convenientlydepressurized prior to its extraction with the aqueous acid phase. Theextraction of the hydroformylation product stream is generally carriedout at temperatures ranging from 20° to 140° C., preferably from 70° to130° C. and more preferably from 90° to 120° C. and under a pressure ofgenerally from 1 to 20 bar, preferably from 1 to 10 bar and morepreferably from 1 to 5 bar. The extraction can be carried out in air orunder an inert gas atmosphere, for example an atmosphere of nitrogen,hydrogen, or argon. However, it may be advantageous to add carbonmonoxide or synthesis gas to the inert gas used or to carry out theextraction in the presence of carbon monoxide.

During extraction the ratio by volume of aqueous to organic phase isgenerally adjusted to from 0.2:1 to 2:1 and preferably from 0.3:1 to1:1. The content of water-soluble, polymeric extracting agents in theaqueous acidic phase is generally from 0.1 to 50%, preferably from 1 to30% and more preferably from 3 to 10%.

During extraction with the acidic aqueous phase there protonizitiontakes place at the tertiary amino group of the ligand, by which meansthe rhodium complexes become water-soluble.

The extracting agents used for the process of the invention are aqueoussolutions of distillable acids, particularly distillable acids whoseammonium salts can be dissociated back to free ligand and free acid attemperatures between room temperature and 200° C.

Particularly suitable extracting agents are aqueous solutions of acidswhose pK_(s) value is 3 to 6. Specific examples thereof are carbonicacid, formic acid, acetic acid, propionic acid, n-butyric acid, orvaleric acid. In the case of carbonic acid, the organic liquid whichcontains the catalyst and which is to be extracted is mixed with wateras described in EP 0,621,075 and carbonic acid gas is forced in.Following phase separation, the desired phase is worked up as describedfor the other acids.

Suitable apparatus for the extraction of the hydroformylation productstream with the aqueous acidic phase comprises virtually allliquid-liquid extractors, for example mixer-settlers, bubble-capcolumns, or counter-flow or parallel-flow extracting columns, wherethese can be equipped with additional internal fittings to improve theefficiency of mixing of the aqueous and organic phases, for examplesieve trays, filling material, or static mixers. The extraction of therhodium catalyst from the hydroformylation product stream can be carriedout in a single stage, but preferably a multistage extraction is used,for example a two-stage or three-stage extraction, in which the aqueousphase containing the chelating agent organic phase is caused to flowparallel to or, more preferably, countercurrently to the organic phase.

On completion of the extraction the hydroformylation product streamfreed from rhodium catalyst can be purified in conventional manner, forexample by distillation, in order to isolate the desired alcohols and/oraldehydes present therein.

In order to liberate the rhodium complexes dissolved in the aqueousextract and to transfer them to an organic phase which can be recycledto the hydroformylation, there is added to the aqueous acidic extract asolvent suitable for the hydroformylation, for example a liquidhydrocarbon or a hydrocarbon mixture such as Texanol® sold by Eastman.Products of the hydroformylation which are suitable for use as solventsor by-products of the hydroformylation are equally suitable. The ratioby volume of the solvent to the aqueous phase is usually from 0.2:1 to2:2 and preferably from 0.5:1 to 1:1 the mixture of solvent and aqueousacid phase is then heated to temperatures such that the ammonium salt ofthe weak acid is dissociated and the, deprotonized rhodium complex isdissolved in the solvent. Following separation of the organic phase fromthe aqueous phase, if present, the organic phase now containing therhodium catalyst is recycled to the hydroformylation stage.

The deprotonization usually takes place with thorough mixing of theorganic and aqueous phases and heating up to, say, 90° C. for theremoval of CO₂ or up to, say, 150° C. for the removal of carboxylicacids, whilst a temperature of 200° C. need not generally be exceeded.

A detailed description of an advantageous embodiment of the process ofthe invention is given below with reference to FIG. 1 by way of example.Obvious details not necessary for illustration of the process of theinvention have been omitted from FIG. 1 for the sake of clarity.

The embodiment shown in FIG. 1 of the process of the invention embracesthe process stages of hydroformylation using a rhodium catalysthomogeneously dissolved in an organic reaction medium, the separation ofthe catalyst from the effluent of the hydroformylation reaction, and thereturn of the rhodium removed from said hydroformylation effluent to thehydroformylation stage. The isolation of the catalyst takes placeoptionally following partial or complete distillation by reversibleextraction of the catalyst from the said effluent or distillationbottoms using an acidic, aqueous phase. Subsequent thermal dissociationof the acid/ligand adduct following extraction, the catalyst isretransferred to an organic phase, by which means the recovery of therhodium without salt formation is guaranteed. The rhodium is thenrecycled to the hydroformylation stage. When the process is carried outcontinuously, it is convenient to carry out catalyst isolation bydistillation alone until the by-products accumulate to such an extentthat extraction becomes necessary.

Specifically, in a continuous embodiment of the process of the inventionas illustrated in FIG. 1, the hydroformylation effluent of thehydroformylated olefin 1 coming from the hydroformylation reactor Hfollowing depressurization and separation of the liquid phase fromexcess synthesis gas is passed either through line 5 to be subjected toextraction processing or through line 2 to be previously subjected to adistillation processing stage (consisting of flash equipment and/or acolumn). The distillation processing stage A causes more readily boilingaldehydes 4 to be separated from high-boiling catalyst-containingbottoms. The bottoms are intermittently or partially passed to theextraction stage via line 6 and intermittently or partially passedthrough line 6 to a stage involving purification by extraction. In saidextraction stage an acidic aqueous phase is mixed with the organic phasein a mixer M. This mixture is fed through line 7 to a phase-separatingstage P. The organic phase comprising aldehydes and/or high-boilingcomponents is separated via line 8 and is available for furtherprocessing. The aqueous phase is passed through line 9 to a mixer M,where it is mixed with an organic phase 10 which can be tolerated by thehydroformylation reaction and which comprises, for example, olefins,aldehydes, and/or alcohols, toluene or other aromatics or blends such asTexanol®, or ethers such as diethyl ether. This mixture is then fedthrough line 11 to be subjected to thermal dissociation in stage T. Thismay be effected, for example, by means of a distillation column to causeseparation of the water/carboxylic acid mixture, or by pure thermaltreatment to eliminate CO₂. The aqueous phase can, if desired, berecycled to the extraction stage via line 12, or it can be removed fromthe system. The catalyst-containing organic phase is recycled to thehydroformylation stage via line 13 the process of the invention isparticularly well suited for the hydroformylation of olefins containingmore than 3, and preferably more than 7 carbon atoms, in particular forthe hydroformylation of C₇ -C₂₀ olefins, which can be straight-chain orbranched-chain and which can contain α-olefinic and/or internal doublebonds, eg octene-1, dodecene-1, trimer- and tetramer-propylene, ordimer- trimer- and tetramer-butylenes. Similarly, unsaturated oligomersof other olefins can be hydroformylated. Likewise different co-oligomersof different olefins. The aldehydes formed from these olefins serve, eg,as intermediates for the preparation of plasticizer alcohols andsurfactants, which can be produced therefrom in conventional manner byhydrogenation . The olefins used for the hydroformylation can beobtained eg by the acid-catalyzed elimination of water from thecorresponding fatty alcohols or according to a large number of othertechnical processes as are described, for example , in Weissermel, Arpe:Industrielle Organische Chemie, pp 67-86, Verlag Chemie, Weinheim, 1978.The process of the invention is also particularly well suited for thehydroformylation of polymeric olefins, for example low molecular weightpolyisobutene, low molecular weight polybutadiene or low molecularweight poly(1,3-butadiene-co-isobutene) orpoly(1,3-butadiene-co-butene). By "low molecular weight polymers" wemean in particular polymers having molecular weights of from 280 bis5000° alton. It is also possible, however, to hydroformylate unsaturatedpolymers of higher molecular weight, ie having molecular weights above5000. The only prerequisite for this is that they must be soluble in thehydroformylation medium.

The present process is thus suitable for the preparation of virtuallyall aldehydes which are obtainable via the hydroformylation of olefins.In particular for example, substituted olefins, which can generallycarry one or two, but preferably one substituent, can also behydroformylated by the process of the invention. For example unsaturatedaliphatic carboxylates, acetals, alcohols, ethers, aldehydes, ketones,and amines and amides can be hydroformylated by the process of theinvention. Those substituted starting olefins which are of interest are,eg, methacrylates, dicyclopentadiene, vinyl ether, and allyl ether andin particular corresponding substituted derivatives of unsaturated fattyacids, for example the esters of oleic, linoleic, linolenic, ricinic, orerucic acid. The aldehydes which can be obtained from these olefinic rawmaterials by hydroformylation are likewise starting materials for thepreparation of biologically readily degradable, surface-activesubstances.

EXAMPLES

A) syntheses of catalyst precursors:5,5'-bis(dimethylaminomethyl)-2,2'bipyridine (ligand 1) is prepared fromβ-picoline in three stages:

1st stage:

the oxidative linkage of 4-picoline to form4,4'-dimethyl-2,2'-bipyridine is described in J. Chem. Soc., DaltonTrans., 1985, pp. 2247.the linkage of β-picoline to form5,5'-dimethyl-2,2'-bipyridine takes place in a very similar manner andwas carried out as described in said reference. ##STR16##

2nd stage:

the free radical bromination of 6,6'-dimethyl-2,2'-bipyridine in CCl₄ inthe presence of a radical starter such as benzoyl peroxide is describedin Helv. Chim. Acta., Vol. 67, pp. 2264, 1984. The bromination of5,5'-dimethyl-2,2'-bipyridine with N-bromosuccinimide in the presence of2,2-azodiisobutyronitrile acting as radical starter takes place in avery similar manner and was carried out as described in said reference.##STR17##

3rd stage:

5,5'-bis(bromomethyl)-2,2'-bipyridine was then caused to react withLiNMe₂ in THF to produce 5,5'-bis(dimethylaminomethyl)-2,2'-bipyridine.The solution was quenched with a 1% strength NaHCO₃ solution and ethylether added until a second phase had formed the purification of theorganic phase yielded the ligand 1. ##STR18##

Alternatively and in analogy to stage 1 a linkage of4-dimethylaminopyridine to produce4,4'-bis(dimethylamino)-2,2'-bipyridine is also possibly. ##STR19## B)General conditions of a batch procedure:

All of the batch hydroformylations effected under a pressure of 70 barwere carried out in an autoclave having a capacity of 100 mL (materialHC). The reaction mixture was heated to reaction temperature over aperiod of 10 min, whilst the solution was stirred vigorously with agas/liquid stirrer. All of the batch hydroformylations effected under apressure of 280 bar were carried out in an autoclave having a capacityof 300 mL (material HC). The reaction mixture was heated to reactiontemperature over a period of 45 min and the solution was stirredvigorously with a magnetic stirrer. The desired pressure was in bothcases adjusted by means of CO/H₂ (1:1), the pressure in the reactorbeing kept at a constant level during the reaction by forcing in moregas as required via a pressure regulator. On conclusion of the reactionthe autoclave was cooled, depressurized, and emptied. An analysis of thereaction mixture was carried out by means of GC--using an internalstandard and correction factors.

Example 1 Hydroformylation with Rh/ligand 1 and separation by extractionwith acetic acid solutions and catalyst recycling

A) In the known hydroformylation of octene-N (isooctene mixture, degreeof branching 1,3; 98 g) with rhodium/ligand 1 (13 ppm of Rh, L/Rh=10,150° C., 280 bar of CO/H₂ 1:1, 5 h, using 5 g of Texanol® acting assolvent) there was obtained a conversion of octenes of 98%, a yield of76% nonanal and of 19% nonanol at a 3% balance loss (based on octene-N).

B) Separation by distillation of the oxo-products at 20 mbar up to abase temperature of 150° C.

C) Repetition of step 1 (12 ppm of Rh), rhodium catalyst/bottomssolution from (b) being used. A conversion of octenes of 99% and a yieldof 66% nonanal and 15% nonanol were obtained at a 16% balance loss(based on octene-N: mechanical losses, formation of high-boilers andparaffin included).

D) Separation by distillation of the oxo-products (99 g) under apressure of 20 mbar up to a base temperature of 150° C. (16 g),extraction of the bottoms with 5% strength acetic acid (1:1 by volume))followed by phase separation. The phase separation was accelerated byfiltration over a kieselguhr bed and a paper filter. 15 ppm of Rh werefound in the organic phase, ie rhodium was extracted with 80%efficiency. Following the introduction of Texanol® to the aqueous phasefollowed by the evaporation of acetic acid/water under standard pressureup to a base temperature of 150° C. there was obtained a homogeneoussolution.

E) Repetition of step 1 (12 ppm of Rh), a rhodium catalyst/Texanol®solution from (d) being used. An octene conversion of 97%, a yield ofnonanal of 67%, and a yield of nonanol of 10.5% was achieved at a 19%balance loss (based on octene-N). The direct high-boiler analysis byseparation, by distillation, of the oxo-products at a temperature of150° C. and under a pressure of 20 mbar indicated only 5% ofhigh-boilers.

F) On carrying out direct extraction of the effluent with 5% strengthacetic acid (3×50 mL) followed by phase separation 3 ppm of Rh werefound in the organic phase, ie rhodium was extracted with 94%efficiency. By introduction of Texanol® to the aqueous phase followed bypurification, by distillation, under standard pressure and up to a basetemperature of 150° C., the ligand was deprotonized.

G) The hydroformylation of a C₁₂ -C₁₄ α-olefin mixture (94 g) withrhodium catalyst/Texanol® solution from (f) (2 ppm of Rh, 100° C., 280bar of CO/H₂ 1:1, 4 h) gave an olefin conversion of 98%, an aldehydeyield of 81%, and a selectivity toward linear isomers of 47% at a 6.5%balance loss (based on α-olefins; mechanical losses, formation ofhigh-boilers and paraffin included).

Example 2 Hydroformylation with Rh/ligand 1 and separation by extractionwith CO₂ /H₂ O solution

a) The hydroformylation of octene-N (isooctene mixture, degree ofbranching 1.3; 95 g) with rhodium/ligand 1 (13 ppm of Rh, L/Rh=10, 150°C., 280 bar of CO/H₂ 1:1 over a period of 5 h in 5 g of Texanol® actingas solvent) gave an octene conversion of 98%, a yield of nonanal plusnonanol of 79%, and an 18% balance loss (based on octene-N).

b) When extraction of the effluent (23 g) from 1 with the addition of 20g of water was carried out by forcing in CO₂ under a pressure of one barof CO₂ followed by phase separation, 4 ppm of Rh were found in theorganic phase and 7 ppm in the aqueous phase. Rhodium was extracted with85% efficiency.

c) Recycling of the rhodium complex took place as described in Example1.

What is claimed is:
 1. A process for the preparation of an aldehyde oran aldehyde and an alcohol by hydroformylation of an olefin containingmore than 3 carbon atoms comprising a hydroformylation stage, in whichthe olefin is hydroformylated under a pressure of from 50 to 1000 barand at a temperature of from 50° C. to 180° C. using a rhodium catalystdissolved in a homogeneous reaction medium and a catalyst recovery stageinvolving extraction of the rhodium catalyst wherein:(a) thehydroformylation is carried out in the presence of a rhodium complex,which has as ligand, a polydentate, organic nitrogen compound that isfree from phosphorus and capable of forming complexes with Group VIIImetals, which additionally contains at least one tertiary nitrogenradical that is capable of being protonized by a weak acid, (b) theeffluent of the hydroformylation stage is subjected to extraction withan aqueous solution of a distillable acid, optionally followingseparation or partial separation of aldehyde and alcohol, (c) theaqueous acid extract is subjected to thermal treatment in the presenceof an organic solvent or solvent mixture which is inert under thehydroformylation conditions, whereby the aqueous acid is distilled offand said complex is deprotonized and transferred to the organic phase,and (d) the organic phase containing the catalyst complex is recycled tothe hydroformylation stage.
 2. A process as defined in claim 1, whereina distillable acid is used the ammonium salts of which can beredissociated into free ligand and free acid at a temperature betweenroom temperature and 200° C.
 3. A process as defined in claim 1, whereinsaid ligand has the formula I: ##STR20## in which X denotes a bridgingmember selected from the group consisting of a covalent bond, methylene,ethylene, oxo, thio, alkylimino, and arylimino and the radicals Rindependently denote hydrogen, an alkyl radical containing from 1 to 18carbon atoms, or an alkoxy radical containing from 1 to 18 carbon atoms,where these radicals may be part of a saturated or unsaturated ring andwhere at least one of the radicals R or, optionally, a substituent onsaid saturated or unsaturated ring formed by said alkyl or alkoxyradicals may be a radical of the formula II: ##STR21## in which n is aninteger from 0 to 20 and R' denotes an alkyl, cycloalkyl, aralkyl, oraryl radical containing not more than 18 carbon atoms, where theradicals R' may be bridged.
 4. A process as defined in claim 1, whereinsaid ligand is a polyamine of the formula III: ##STR22## in which R"denotes hydrogen, an alkyl, cycloalkyl, aryl, or aralkyl radical, whichcan in turn carry a dialkylamino radical, and m is an integer from 2 to35000, provided that when R" denotes hydrogen at least some of thehydrogen atoms are substituted by alkyl carbonyl containing from 2 to 18carbon atoms or by a hydroxy(alkoxy)alkyl radical obtained by reactionof the secondary amino group with from 1 to 10 mol of ethylene oxide orfrom 1 to 10 mol of propylene oxide, and further provided that thepolyamine contains at least 3 tertiary nitrogen atoms capable of beingprotonized.
 5. A process as defined in claim 3, wherein said ligand is abipyridine of the formula IV: ##STR23## in which at least one of theradicals R or, optionally, the substituents on said saturated orunsaturated rings is a tertiary amino group-containing radical of theformula II: ##STR24## in which n and R' have the meanings stated inclaim
 3. 6. A process as defined in claim 1, wherein the ligand used isa compound of the formula: ##STR25## in which the radical: ##STR26## isattached to the pyridyl ring in position 4,4' or 5,5' and in which theradicals R' independently denote an alkyl, cycloalkyl, aralkyl, or arylradical containing not more than 18 carbon atoms.
 7. A process asdefined in claim 1, wherein the extraction is carried out using an acidhaving a pK value of from 3 to
 6. 8. A process as defined in claim 1,wherein the extraction is carried out using an aqueous solution ofcarbonic acid, formic acid, acetic acid, propionic acid, n-butyric acid,or n-valeric acid.
 9. A process as defined in claim 1, wherein an olefincontaining from 7 to 20 carbon atoms or polyisobutene ishydroformylated.